We present LibRA, a streamlined radio astronomy library that demonstrates how modern software engineering practices can transform computational astronomy workflows. Extracted from CASA’s algorithmic core while eliminating non-essential dependencies, LibRA implements a robust software stack built on C++ STL interfaces, enabling both high performance and broad accessibility. Our approach prioritizes software maintainability through a comprehensive DevOps pipeline featuring automated CI/CD testing across CPU and GPU architectures on RHEL8/9 and Ubuntu platforms, with deployment flexibility via CMake builds, containerization, and Spack package management.

Context. In radio interferometry, images are recovered from incompletely sampled Fourier datasets. The de facto standard algorithm, the Cotton–Schwab CLEAN, iteratively switches between computing a deconvolution (minor loop) and subtracting the model from the visibilities (major loop). Aims. The next generation of radio interferometers is expected to handle much higher data rates, image sizes, and sensitivity, making acceleration of current data processing algorithms necessary. We aim to achieve this by evaluating the potential of various well-known acceleration techniques in convex optimization for the major loop. For the present manuscript, we limit our study of these techniques to the CLEAN framework. Methods. To this end, we identify CLEAN with a Newton scheme and work backwards through this chain of arguments to express Nesterov acceleration and conjugate gradient orthogonalization in the major and minor loop framework. Results. The resulting algorithms are simple extensions of the traditional framework. However, they converge multiple times faster than traditional techniques and reduce the residual significantly deeper. These improvements achieved by accelerating the major loop are competitive with other well-known improvements by replacing the minor loop with more advanced algorithms, but at lower numerical cost. The best performance is achieved by combining these two developments. Conclusions. CLEAN remains among the fastest and most robust algorithms for imaging in radio interferometry and can be easily extended to achieve an order of magnitude faster convergence speed and dynamic range. The procedure outlined in this manuscript is relatively straightforward and could be easily extended.

Radio interferometric imaging with current and future instruments requires the handling of large datasets. GPUs provide an effective means of dealing with this data deluge. However, to fully leverage the computational power available on these GPUs, a tightly coupled iterative approach involving performance engineering and software engineering is required.

The MeerKAT Absorption Line Survey (MALS) has observed 391 telescope pointings at L-band (900 - 1670 MHz) at $\delta\lesssim$ $+20\deg$. We present radio continuum images and a catalog of 495,325 (240,321) radio sources detected at a signal-to-noise ratio (SNR) $>$5 over an area of 2289 deg$^2$ (1132 deg$^2$) at 1006 MHz (1381 MHz). Every MALS pointing contains a central bright radio source ($S_{1\,\mathrm{GHz}} \gtrsim 0.2$ Jy). The median spatial resolution is $12^{\prime\prime}$ ($8^{\prime\prime}$). The median rms noise away from the pointing center is 25 $\mu$Jy beam$^{-1}$ (22 $\mu$Jy beam$^{-1}$) and is within $\sim$ 15% of the achievable theoretical sensitivity. The flux density scale ratio and astrometric accuracy deduced from multiply observed sources in MALS are less than 1% (8% scatter) and $1^{\prime\prime}$, respectively. Through comparisons with NVSS and FIRST at 1.4 GHz, we establish the catalog's accuracy in the flux density scale and astrometry to be better than 6% (15% scatter) and $0.8^{\prime\prime}$, respectively. The median flux density offset is higher (9%) for an alternate beam model based on holographic measurements. The MALS radio source counts at 1.4 GHz are in agreement with literature. We estimate spectral indices ($\alpha$) of a subset of 125,621 sources (SNR$>$8), confirm the flattening of spectral indices with decreasing flux density and identify 140 ultra steep-spectrum ($\alpha<-1.3$) sources as prospective high-$z$ radio galaxies ($z>2$). We have identified 1308 variable and 122 transient radio sources comprising primarily of AGN that demonstrate long-term (26 years) variability in their observed flux densities. The MALS catalogs and images are publicly available at https://mals.iucaa.in.

The ngVLA is a new interferometric radio astronomy facility with transformative capabilities, being developed by the National Radio Astronomy Observatory. It combines two orders of magnitude in frequency coverage, over 1.2-116 GHz, with unprecedented sensitivity, spatial resolution and spatial frequency coverage, opening up new discovery space, impacting nearly every area of astrophysics. The high sensitivity that enables the path breaking science goals, which in turn lead to stringent instrument requirements, also open up new approaches to meeting them, previously only possible in limited contexts. Chief among the requirements are the image dynamic range specifications of 45 dB and 35 dB at 8 GHz and 27 GHz in single pointing and mosaiced observations. As its baseline calibration strategy to meet these requirements, we leverage the sensitivity through routine use of self-calibration on short time scales to counter atmospheric delay fluctuations and pointing self-calibration to correct for pointing errors. This presentation provides the bases for these approaches and the case for their application to the ngVLA.

We present X-ray and radio observations of the recently-discovered bow shock pulsar wind nebula associated with PSR J0002+6216, characterizing the PWN morphology, which was unresolved in previous studies. The multi-frequency, multi-epoch Very Large Array radio observations reveal a cometary tail trailing the pulsar and extending up to 5.3', with multiple kinks along the emission. The presented radio continuum images from multi-configuration broadband VLA observations are one of the first results from the application of multi-term multi-frequency synthesis deconvolution in combination with the awproject gridder implemented in the Common Astronomy Software Applications package (CASA). The X-ray emission observed with Chandra extends to only 21”, fades quickly, and has some hot spots present along the extended radio emission. These kinks could indicate the presence of density variation in the local ISM or turbulence. The bow shock standoff distance estimates a small bow shock region with a size 0.003-0.009 pc, consistent with the pulsar spin-down power of Edot=1.51x10^35 ergs/s estimated from timing. The high-resolution radio image reveals the presence of an asymmetry in the bow shock region which is also present in the X-ray image. The broadband radio image shows an unusually steep spectrum along with a flat-spectrum sheath, which could indicate varying opacity or energy injection into the region. Spatially-resolved X-ray spectra provide marginal evidence of synchrotron cooling along the extended tail. Our analysis of the X-ray data also shows that this pulsar has a low spin-down power and one of the lowest X-ray efficiencies observed in these objects.

CASA, the Common Astronomy Software Applications, is the primary data processing software for the Atacama Large Millimeter/submillimeter Array (ALMA) and the Karl G. Jansky Very Large Array (VLA), and is frequently used also for other radio telescopes. The CASA software can handle data from single-dish, aperture-synthesis, and Very Long Baseline Interferometery (VLBI) telescopes. One of its core functionalities is to support the calibration and imaging pipelines for ALMA, VLA, VLA Sky Survey (VLASS), and the Nobeyama 45m telescope. This paper presents a high-level overview of the basic structure of the CASA software, as well as procedures for calibrating and imaging astronomical radio data in CASA. CASA is being developed by an international consortium of scientists and software engineers based at the National Radio Astronomical Observatory (NRAO), the European Southern Observatory (ESO), the National Astronomical Observatory of Japan (NAOJ), and the Joint Institute for VLBI European Research Infrastructure Consortium (JIV-ERIC), under the guidance of NRAO.

In this third paper of a series describing direction-dependent corrections for polarimetric radio imaging, we present the the A-to-Z solver methodology to model the full Jones antenna aperture illumination pattern (AIP) using Zernike polynomials. In order to achieve accurate, thermal noise-limited imaging with modern radio interferometers, it is necessary to correct for the instrumental effects of the antenna primary beam (PB) as a function of time, frequency, and polarization. The algorithm employs the orthonormal, circular Zernike polynomial basis to model the full Jones AIP response, which is obtained by a Fourier transform of corresponding antenna holography measurements. These full Jones models are then used to reconstruct the full Mueller AIP response of an antenna, in principle accounting for all the off-axis frequency-dependent leakage effects of the PB. The A-to-Z solver is general enough to accommodate any interferometer for which holographic measurements exist, and we have successfully modeled the AIP of the VLA, MeerKAT, and ALMA as a demonstration of its versatility. We show that our models capture the PB morphology to high accuracy within the first two side lobes, and show the viability of full Mueller gridding and deconvolution for any telescope given high-quality holographic measurements.

We present details of the Automated Radio Telescope Imaging Pipeline (ARTIP) and the results of a sensitive blind search for H i and OH absorbers at z < 0.4 and z < 0.7, respectively. ARTIP is written in Python 3.6, extensively uses the Common Astronomy Software Application tools and tasks, and is designed to enable the geographically distributed MeerKAT Absorption Line Survey (MALS) team to collaboratively process large volumes of radio interferometric data. We apply it to the first MALS data set obtained using the 64-dish MeerKAT radio telescope and 32 K channel mode of the correlator. With merely 40 minutes on target, we present the most sensitive spectrum of PKS 1830-211 ever obtained and characterize the known H i (z = 0.19) and OH (z = 0.89) absorbers. We further demonstrate ARTIP's capabilities to handle realistic observing scenarios by applying it to a sample of 72 bright radio sources observed with the upgraded Giant Metrewave Radio Telescope (uGMRT) to blindly search for H i and OH absorbers. We estimate the numbers of H i and OH absorbers per unit redshift to be n21(z ∼ 0.18) < 0.14 and nOH(z ∼ 0.40) < 0.12, respectively, and constrain the cold gas covering factor of galaxies at large impact parameters (50 kpc < ρ < 150 kpc) to be less than 0.022. Due to the small redshift path, Δz ∼ 13 for H i with column density >5.4 × 1019 cm−2, the survey has probed only the outskirts of star-forming galaxies at ρ > 30 kpc. MALS with the expected Δz ∼ 103–4 will overcome this limitation and provide stringent constraints on the cold gas fraction of galaxies in diverse environments over 0 < z < 1.5.

We present the DSA-2000: a world-leading radio survey telescope and multi-messenger discovery engine for the next decade. The array will be the first true radio camera, outputting science-ready image data over the 0.7 - 2 GHz frequency range with a spatial resolution of 3.5 arcsec. With 2000 x 5 m dishes, the DSA-2000 will have an equivalent point-source sensitivity to SKA1-mid, but with ten times the survey speed. The DSA-2000 is envisaged as an all-sky survey instrument complementary to the ngVLA, and as a counterpart to the LSST (optical), SPHEREx (near-infrared) and SRG/eROSITA (X-ray) all-sky surveys. Over a five-year prime phase, the DSA-2000 will image the entire sky above declination -30 degrees every four months, detecting > 1 unique billion radio sources in a combined full-Stokes sky map with 500 nJy/beam rms noise. This all-sky survey will be complemented by intermediate and deep surveys, as well as spectral and polarization image cubes. The array will be a cornerstone for multi-messenger science, serving as the principal instrument for the US pulsar timing array community, and by searching for radio afterglows of compact object mergers detected by LIGO and Virgo. The array will simultaneously detect and localize ~10,000 fast radio bursts each year, realizing their ultimate use as a cosmological tool. The DSA-2000 will be proposed to the NSF Mid-Scale Research Infrastructure-2 program with a view to first light in 2026

We have carried out Very Large Array imaging and a Fermi timing analysis of the 115 ms γ -ray and radio pulsar PSR J0002+6216. We found that the pulsar lies at the apex of a narrowly collimated cometary-like 7′ tail of nonthermal radio emission, which we identify as a bow-shock pulsar wind nebula. The tail of the nebula points back toward the geometric center of the supernova remnant CTB 1 (G116.9+0.2) 28′ away, at a position angle θ μ = 113°. We measure a proper motion with 2.9 σ significance from a Fermi timing analysis giving μ = 115 ± 33 mas yr −1 and θ μ = 121° ± 13°, corresponding to a large transverse pulsar velocity of 1100 km s −1 at a distance of 2 kpc. This proper motion is of the right magnitude and direction to support the claim that PSR J0002+6216 was born from the same supernova that produced CTB 1. We explore the implications for pulsar birth periods, asymmetric supernova explosions, and mechanisms for pulsar natal kick velocities.

The sensitivity of modern radio telescopes is high enough that imaging is often limited by the effects of variations in the antenna primary beams as a function of frequency, polarization, time or antenna. The WB Full-polarization AW-Projection (WB-FP-AWP) algorithm offers a method to correct for the effects of antenna primary beams, which requires an accurate model of the antenna aperture illumination patterns (AIP), as a function of time, frequency, and polarization. The AIP is usually referred to in the literature as the A-term. This report details the development of an algorithm to model the antenna aperture illumination pattern. To model complex-valued aperture illumination patterns in full polarization an algorithm using Zernike Polynomials was tested against holographic measurements of the EVLA, ALMA and MeerKAT telescopes and demonstrated to achieve the required accuracy. Since this is a polynomial model, it is applicable to any type of antenna (as demonstrated by application to EVLA, ALMA and MeerKAT – which have very different type of antennas). The algorithm implementation was done in Python. More work is necessary to incorporate this work for use as part of the WB-FP-AW-Projection algorithm for imaging, which will enable its use for wide-field, wide-band, polarimetric imaging with MeerKAT.

In the last few years the development of Python code for science and data reduction purposes has gained significant popularity. ESO itself uses a Python-based archiving system for VLT and ALMA data. Also the data reduction suite for ALMA data is python-based. Rapid development is fostered by a big community and a wide range of already available packages. However Python enforces locking mechanisms, to ensure thread safety, that effectively reduce the capacity of Python to use only one core. In this context a number of alternatives have been developed by the community to emulate actual multi-threading and make parallel processing easier to use from Python, preserving interactivity.

CASA, the Common Astronomy Software Applications package, is the primary data processing software for the Atacama Large Millimeter/submillimeter Array (ALMA) and NSF's Karl G. Jansky Very Large Array (VLA), and is frequently used also for other radio telescopes. The CASA software can process data from both single-dish and aperture-synthesis telescopes, and one of its core functionalities is to support the data reduction and imaging pipelines for ALMA, VLA and the VLA Sky Survey (VLASS). CASA has recently undergone several exciting new developments, including an increased flexibility in Python (CASA 6), support of Very Long Baseline Interferometry (VLBI), performance gains through parallel imaging, data visualization with the new Cube Analysis Rendering Tool for Astronomy (CARTA), enhanced reliability and testing, and modernized documentation. These proceedings of the 2019 Astronomical Data Analysis Software & Systems (ADASS) conference give an update of the CASA project, and detail how these new developments will enhance user experience of CASA.

CASA, the Common Astronomy Software Applications package, is the primary data processing software for the Atacama Large Millimeter/submillimeter Array (ALMA) and the Karl G. Jansky Very Large Array (VLA), and is frequently used also for other radio telescopes. In these proceedings of the 28th Astronomical Data Analysis Software & Systems (ADASS) conference, we give an overview of several new features in the CASA imaging task TCLEAN. This includes improved automated masking for image deconvolution, as well as parallel imaging options to increase imaging speeds. In addition, we highlight two upcoming developments. The first is the anticipated arrival of a first-look version of the Cube Analysis and Rendering Tool for Astronomy (CARTA), which is expected to eventually replace the CASA VIEWER. The other is a change in the way the different CASA components (e.g., tools and tasks) can be integrated within the Python environment, allowing much greater flexibility for users starting with CASA 6. We also summarize a list of CASA links to guide the user community to the latest CASA information and documentation.

Deep galaxy surveys have revealed that the global star formation rate (SFR) density in the Universe peaks at 1 < z < 2 and sharply declines towards z = 0. But a clear picture of the underlying processes, in particular the evolution of cold atomic ( 100 K) and molecular gas phases, that drive such a strong evolution is yet to emerge. MALS is designed to use MeerKAT's L- and UHF-band receivers to carry out the most sensitive (N(HI)>10^19 cm^-2) dust-unbiased search of intervening HI 21-cm and OH 18-cm absorption lines at 0 < z < 2. This will provide reliable measurements of the evolution of cold atomic and molecular gas cross-sections of galaxies, and unravel the processes driving the steep evolution in the SFR density. The large sample of HI and OH absorbers obtained from the survey will (i) lead to tightest constraints on the fundamental constants of physics, and (ii) be ideally suited to probe the evolution of magnetic fields in disks of galaxies via Zeeman Splitting or Rotation Measure synthesis. The survey will also provide an unbiased census of HI and OH absorbers, i.e. cold gas associated with powerful AGNs (>10^24 W Hz^-1) at 0 < z < 2, and will simultaneously deliver a blind HI and OH emission line survey, and radio continuum survey. Here, we describe the MALS survey design, observing plan and the science issues to be addressed under various science themes.

The effects of the antenna far-field power pattern limits the imaging performance of modern wide-bandwidth, high-sensitivity interferometric radio telescopes. Given a model for the aperture illumination pattern (AIP) of the antenna, referred to as the A-term, the wide-band (WB) A-Projection algorithm corrects for the effects of its time, frequency, and polarization structure. The level to which this correction is possible depends on how accurately the A-term, represents the true AIP. In this paper, we describe the A-Solver methodology that combines physical modeling with optimization to holographic measurements to build an accurate model for the AIP. Using a parametrized ray-tracing code as the predictor, we solve for the frequency dependence of the antenna optics and show that the resulting low-order model for the Karl G. Jansky Very Large Array (VLA) antenna captures the dominant frequency-dependent terms. The A-Solver methodology described here is generic and can be adapted for other types of antennas as well. The parameterization is based on the physical characteristics of the antenna structure and optics and is therefore arguably a compact representation (minimized degrees of freedom) of the frequency-dependent structure of the antenna A-term. In this paper, we also show that the parameters derived from A-Solver methodology are expected to improve sensitivity and imaging performance out to the first side-lobe of the antenna.

N. Gupta∗1, R. Srianand1, W. Baan2, A. Baker3, R. Beswick4, S. Bhatnagar5, D. Bhattacharya1, A. Bosma6, C. Carilli5, M. Cluver7, F. Combes8, C. Cress9, R. Dutta1, J. Fynbo10, G. Heald11, M. Hilton12, T. Hussain1, M. Jarvis7,13 G. Jozsa14, P. Kamphuis15, A. Kembhavi1, J. Kerp16, H.-R. Klöckner17, J. Krogager18, V. Kulkarni19, C. Ledoux20, A. Mahabal21, T. Mauch14, K. Moodley12, E. Momjian5, R. Morganti2, P. Noterdaeme18, T. Oosterloo2, P. Petitjean18, A. Schröder22, P. Serra23, J. Sievers12, K. Spekkens24, P. Väisänen22, T. van der Hulst25, M. Vivek26, J. Wang11, O.I. Wong27 and A.R. Zungu12 1 Inter-University Centre for Astronomy and Astrophysics, India; (see Appendix A for author affiliations.) E-mail: ngupta@iucaa.in